An integral field spectrograph for SNAP supernova studies Page: 3 of 10
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Property Visible IR
Wavelength coverage ( m) 0.35-0.98 0.98-1.70
Field of view 3.0" x 3.0" 3.0" x 3.0"
Spatial resolution element (arcsec) 0.15 0.15
Number of slices 20 20
Spectral resolution, X/SX 100 100
Table 1: Spectrograph main specifications.The field of view should include the
underlying galaxy in order to determine
its spectrum during the same exposure.
This is necessary for subtraction of the
host spectrum from the spectrum in the
supernovae region. Based on the mean
size of galaxies at redshift 1-2, a 3"x3"
field of view is sufficient.Space instruments must be light and
compact, and must minimize interfaces with the spacecraft. To reduce the time budget, we must take the galaxy and SN
spectra in the same exposure and push to the highest efficiency possible for the highest redshifts.
3 INSTRUMENT CONCEPT TRADE-
OFFGiven the science drivers and requirements, we
conducted a trade study to choose the best instrument
concept. The requirement for simultaneous
acquisition of SN and host spectra, and the high
object acquisition precision that would be needed for
a traditional long slit spectrograph, lead us to prefer a
3D spectrograph. A 3D spectrograph reconstructs the
data cube including the two spatial directions X and
Y plus the wavelength direction as shown in Figure 2.
For each spatial pixel, the spectrum is reconstructed.
Thanks to the 3"x3" field of view, the pointing
requirements are relaxed and the galaxy and SN data
are acquired at the same time. Two principal
techniques are indicated for 3D spectroscopy: first,
the use of a Fourier Transform Spectrometer (FTS),
and second, the use of integral field spectroscopy.
The FTS technique is based on the classical
Michelson interferometer principle. When one of the
two flat mirrors is moved, the Fourier transform
space of the wavelength is scanned. Herschel is using
this technique. But the domain of excellence for the
FTS is at longer wavelengths, smaller wavelength
range, and higher spectral resolution than SNAP
needs. The main drawback to an FTS on SNAP
would be the need for a translating device with a
quarter-millimeter throw and a positioning accuracy
of a few nanometers. This would call for a complex
mechanism, and for a very precise metrology system.
Integral field spectroscopy using traditional
dispersers is based on three generic techniques as
shown in Figure 3. The simplest one is the use of
classical microlenses in order to create an image ofx
Figure 2: 3D spectroscopy illustration.
Telescope Spectrograph Spectrograph
focal surface input output spectrum
Pupil QQQQ
Lenslets imgery Q Q o Q
Detector
Lenslets Fibres slit
+ fibres ] ->LLJ
Image 1 z3 4 1 slit
slicer M
4
Only the image slicer retains spatial
information within each slice/sample
Figure 3: Integral Field Spectroscopy illustration.~
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Ealet, Anne; Prieto, E.; Bonissent, A.; Malina, R.; Basa, S.; LeFevre, O. et al. An integral field spectrograph for SNAP supernova studies, article, July 29, 2002; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc734403/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.